This invention relates generally to miniature switches and potentiometers, and particularly to a combined push-pull switch and rotary potentiometer volume control assembly for use in hearing aids and similar devices.
Hearing aids and their components are well known to the art, with many technological advances having been made in the functional capabilities of such devices, as well as in those aesthetic features which are of critical importance in the particularly competitive marketplace.
In general, hearing aids may be divided into three broad categories: larger amplifiers carried in an individual's pocket or attached to a belt and having a cable-connected earphone; "behind-the-ear" units in which a microphone and amplifier are contained in a curved case held behind the ear with a speaker or earphone positioned in or near the opening of the ear canal; and "in-the-canal" models wherein the entire hearing aid (including the microphone, amplifier, and speaker) are self-contained and inserted within the ear canal.
As the size of the hearing aid decreases, the cost of the electronic components will generally increase and the capabilities of the hearing aid will decrease proportionately. This is not to suggest that smaller in-the-canal type hearing aids cannot be extremely effective nor include many features of larger hearing aids, but simply reflects the fact that the difficulty and expense of designing and manufacturing miniaturized versions of more complex filters or more powerful amplifiers will generally lead to a more expensive overall unit. Consequently, there is a balancing between the miniaturization of the hearing aid, the inclusion of options which would enhance the amplification or quality of sound reproduction, and the cost of the hearing aid. The features and capabilities required in a particular hearing aid also depend upon the needs of the user as dictated by their degree of hearing impairment, the environment in which the hearing aid will be used, and the personal preferences of the purchaser.
Behind-the-ear hearing aids, which are somewhat larger and more visible but can provide a higher measure of amplification and sound quality at a lower price, are more popular in European countries where socialized medicine largely controls health care expenditures. In the United States and other countries, however, where consumers determine what features and styles they prefer and can afford and where cosmetic considerations are taken into greater account, in-the-canal hearing aids are more popular and widely used.
It is therefore of critical importance, particularly with in-the-canal type hearing aids, to utilize the available space as efficiently as possible, and to make each component of the unit function optimally.
Improvements are continually being made, not only in the fundamental electronic components of hearing aids such as microphones, amplifiers, or speakers, but also in peripheral components such as the battery or battery case, sound conducting channel, switches, controls, as well as other aesthetic and cosmetic factors.
One particular area of development has been in the switches used to turn the hearing aids on or off, and those controls responsible for varying the gain or volume level and other acoustical characteristics of the amplification circuits.
A noteworthy improvement along this line has been the incorporation of a rotary potentiometer and common switch into an integral assembly, such that one component can be used for both power control and gain adjustment. Representative examples of such assemblies may be seen in U.S. Pat. Nos. 3,629,780; 4,081,782; and 4,117,444. A similar and related improvement disclosed in U.S. Pat. No. 4,649,366 was the inclusion of a trimmer control within the potentiometer knob.
Although each of these examples presents a general advance in the art, each of the disclosed structures possess some common drawbacks and disadvantages.
The switches or potentiometer knobs for volume control are generally mounted close to flush with the surface of the hearing aid, and are therefore equipped with radially projecting fins or serrated teeth to facilitate rotation of the knobs. Despite such measures, these controls remain difficult to adjust accurately since they are too small or too close to the surface of the hearing aid to be pinched between the fingers, a method allowing for finer adjustment.
Further, the mechanical components of such switch and potentiometer assemblies are so complex and fragile that the potentiometer knobs have a tendency to break or be accidentally pulled off the hearing aid during normal use. While such a problem might be expected more with the raised potentiometer knobs of the type shown in the '780 patent listed above, in which the knob is held in place by a thin stop plate and sealed above a slightly flared segment of the driver, it is encountered with almost all potentiometer and switch assemblies including those which are nearly flush mounted. One proposed solution to this problem is disclosed in U.S. Pat. No. 3,549,828 showing a retaining ring which securely mounts the switch and potentiometer assembly in the hearing aid housing.
While many of the rotary potentiometers and switch assemblies disclosed are rotated to turn the switch on or off, an alternative has been to place the on-off switch in combination with the battery compartment. One method has been to insert the battery into a hinged clip which can pivot in and out of a recessed well within the hearing aid. In this case, the cover of the battery compartment forms a handle which may be gripped by a person's fingers, and the process of pivoting the battery clip from the compartment breaks the electrical contact to the battery and turns off the power. Variations on this idea are shown in U.S. Pat. Nos. 3,475,566 and 4,634,815 which disclose an integral toggle switch within the battery compartment of a behind-the-ear hearing aid, and a rotatable push-button switch and potentiometer assembly housed within the battery compartment cover, respectively.
The '815 patent states that such a control provides a single but relatively large operating element, a factor which may make such a control undesirable for many applications. Furthermore, the particular design of the '815 switch and potentiometer mitigates against the use of serrations or gripping aids, and prevents a user from pinching the potentiometer knob between his fingers to make finer adjustments. The alternative, as in the case of the '566 patent, is to have separate controls on the face plate, which is less efficient.
Another area of development has been the structural features used to insert and remove the hearing aid from the ear canal. As hearing aids are made progressively smaller and less obtrusive, they are similarly designed to be inserted further into the ear canal, and form a more secure engagement therewith, to enhance their acoustic transmission. Consequently, it is necessary to provide some means for the user to easily remove the hearing aid from the ear canal for washing, sleeping, adjustments, and servicing.
One example of such a device is shown in U.S. Pat. No. 4,565,904 which discloses a pivotally hinged removal handle mounted in the face plate of a hearing aid adjacent the battery compartment cover. This handle may be made of a transparent plastic resin so as to be less visible, and may be pivoted outwardly to an extended position with a fingernail, and then gripped between the user's fingertips.
To be functional, however, such a removal handle must be much larger than shown in the drawings of the '904 patent, and the hinge assembly and metal pin necessary to secure the handle in place consumes a major portion of the surface of the face plate, further congesting the control panel and limiting the space available for other components. Despite the size of the removal handle, it remains subject to being broken or snapped off at its thinner regions due to the twisting or prying force applied by the user when removing the hearing aid.